U.S. patent application number 13/262383 was filed with the patent office on 2012-02-09 for call control.
Invention is credited to Philip L. Eardley, Simon PA Ringland, Matthew D. Walker.
Application Number | 20120033798 13/262383 |
Document ID | / |
Family ID | 40671956 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120033798 |
Kind Code |
A1 |
Eardley; Philip L. ; et
al. |
February 9, 2012 |
CALL CONTROL
Abstract
A method of call control in which a first communications
network, detecting calls directed to a destination in the first
network; redirects at least some of the calls to a destination in a
second network (e.g. on no answer from the destination in the first
network). The first network then operates in two phases. In a first
phase, for a group of calls redirected to the second network, the
time delay before the call is answered in the second network is
recorded. When a number of time delays have been recorded, a delay
period is set to a value less than the maximum value of the
recorded time delays. In a second phase, for a second group of
calls redirected to the second network subsequent to the calls of
the first group, when a call of the second group is not answered in
the second network within the delay period, the call is redirected
to a message service associated with the first network.
Inventors: |
Eardley; Philip L.;
(Ipswich, GB) ; Ringland; Simon PA; (Ipswich,
GB) ; Walker; Matthew D.; (Felixstowe, GB) |
Family ID: |
40671956 |
Appl. No.: |
13/262383 |
Filed: |
March 11, 2010 |
PCT Filed: |
March 11, 2010 |
PCT NO: |
PCT/GB10/00444 |
371 Date: |
September 30, 2011 |
Current U.S.
Class: |
379/211.01 ;
379/220.01 |
Current CPC
Class: |
H04M 2201/12 20130101;
H04M 3/54 20130101; H04M 2201/14 20130101; H04M 2201/36 20130101;
H04M 7/1225 20130101 |
Class at
Publication: |
379/211.01 ;
379/220.01 |
International
Class: |
H04M 3/42 20060101
H04M003/42; H04M 7/00 20060101 H04M007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2009 |
GB |
0905456.0 |
Claims
1. A method of call control including, in a first network,
detecting calls directed to a destination in the first network;
redirecting a plurality of the calls to a destination in a second
network; in a first phase, for each call of a first set of the
plurality of calls redirected to the second network, recording the
time delay before the call is answered in the second network; and
setting a delay period to a value less than the maximum value of
the time delays recorded in the first phase; in a second phase, for
a second set of the plurality of calls, comprising calls redirected
to the second network subsequent to the calls of the first set,
when a call of the second set redirected to the second network is
not answered in the second network within the delay period,
redirecting in the first network the call to an alternative
destination associated with the first network.
2. The method of claim 1, in which each time delay is measured in
the first network starting from receipt by the first network of
information from the second network indicating that a ringing
signal for the redirected call has been applied to the destination
in the second network.
3. The method of claim 1, in which each time delay is measured in
the first network starting from the transfer by the first network
of the call to the second network.
4. The method of claim 1, in which each time delay is measured in
the first network terminating on receipt by the first network of
information from the second network indicating that the redirected
call has been answered in the second network.
5. The method of claim 1, in which the delay period is set to a
value equal to one of one second and one ring period less than the
maximum value of the recorded time delays.
6. The method of claim 1 including, when a call of the second set
redirected to the second network is answered in the second network
within a second delay period shorter than the delay period,
redirecting in the first network the call to an alternative
destination associated with the first network.
7. The method of claim 1, in which the recording of time delays is
carried out by a call management system remote from the user.
8. The method of claim 1, in which the delay period is increased
over time until the redirection of calls of the second set to the
alternative destination associated with the first network ceases;
at which point, the delay period is decreased over time until the
redirection of calls of the second set to the alternative
destination associated with the first network recommences.
9. The method of claim 8 including, upon detection of a sequence of
calls of the second set, none of which is redirected to the
alternative destination associated with the first network,
resetting the delay period.
10. The method of claim 1, in which the first phase is repeatedly
periodically to provide a revised value of the delay period for use
in a new occurrence of the second phase.
11. The method of claim 1 including, upon detection of a sequence
of calls of the second set, none of which is redirected to the
alternative destination associated with the first network,
repeating the first phase and resetting the delay period.
12. The method of claim 1, in which the destination in the first
network comprises a terminal operated by a first user and the
destination in the second network comprises a terminal operated by
a second user.
13. The method of claim 1, in which the alternative destination
associated with the first network comprises a message service.
14. A first communications network comprising a network controller
arranged in use to detect calls directed to a destination in the
first network; and to redirect a plurality of the calls to a
destination in a second network; in which the network controller
comprises: a first timer arranged in use to record the time delay
before each call of a first set of the plurality of calls
redirected to the second network is answered in the second network;
a timer controller arranged in use to set a second timer to a delay
period value less than the maximum value of the recorded time
delays; and a switch arranged in use to redirect an unanswered call
to an alternative destination associated with the first network; in
which an unanswered call is a call from a second set of the
plurality of calls, comprising calls redirected to the second
network subsequent to the calls of the first set that is not
answered in the second network within the delay period.
15. A first communications network as claimed in claim 14 in which
the timer controller is arranged in use to set a third timer to a
second delay period shorter than the delay period; in which the
switch is arranged in use to redirect a call that is answered in
the second network within the second delay period to an alternative
destination associated with the first network.
16. A computer readable medium storing processor executable
instructions for causing the method of claim 1 to be carried out
when run on a general purpose computer.
Description
[0001] The present invention relates to the field of telephony
networks in general and to the control of calls in telephony
networks in particular.
[0002] An increasing number of telephone subscribers have more than
one telephony account, benefiting from the increased flexibility
and improved accessibility that multiple accounts can provide. For
example, a subscriber may have a first, Wi-Fi telephony account and
a second, GSM telephony account (a list of acronyms is provided at
the end of the description). In such a telephony system, the Wi-Fi
account can often be out of operation either because the Wi-Fi
handset is switched off or is out of range of the nearest Wi-Fi
access point (or "hotspot"). It is therefore convenient for the
user, when their Wi-Fi telephony account is unavailable, for calls
directed to the user at their Wi-Fi account to be redirected to a
second telephony account, e.g. one provided via the GSM networks. A
problem arises in the case of such re-directed calls when the call
is not answered at the handset operating on the second network to
which the call has been redirected. The default behaviour of a
telephony system in this situation would be for the call to be
forwarded to a messaging service, e.g.: voicemail service,
associated with the handset in the second network, to which the
call has been diverted. This behaviour, however, can lead to
confusion for the user with messages, which should be associated
with, and directly accessible from, their Wi-Fi handset, being
instead associated with their GSM handset. The default behaviour
can also result in extra cost to the user where the user is liable
to pay the mobile operator for a second diversion from the mobile
network back to the redirecting network. Similar problems can occur
with other combinations of telephony account, such as GSM with
PSTN, where calls to the user may be redirected to the PSTN, when
the user's GSM handset is switched off or out of range of a GSM
transmitter.
[0003] The behaviour described above may be less of a problem where
both handsets are provided by the same service provider. Published
patent application US 2007/0070976 describes a telecommunication
system in which a service provider provides both a mobile network
and a VoIP network interlinked via a PSTN backbone. Both networks
provide telephony services to a user. According to this
telecommunication system, calls to the user directed to a terminal
on the fixed network may be delivered to a terminal associated with
that user on the mobile network. If the call is not completed to
the second terminal on the mobile network, the mobile network is
able to detect this and to return the call to the fixed network,
where it is forwarded to a messaging service on the fixed
network.
[0004] The telecommunication system of US'976 should work for users
who have dual accounts from the same service provider. For example,
"TruPhone" from Software Cellular Network, London, England is a
service that provides a software application for mobile phones.
This application provides end-users with a second Voice-over IP
account, which works alongside an existing mobile phone account. In
practice, not all users will have dual accounts from the same
service provider and not all networks will be set up like the
second network of US'976. In a situation where the user has a first
account with a first service provider operating a first network and
a second account with a second service provider operating a second
network, the above system may not work if, as is likely, there is
no overall, control mechanism that allows the second network to be
aware that an incoming call has been redirected from another
network or to be alert to the need to return the call, if
unanswered, to a messaging service in the other network.
[0005] A method of call control and a call control system is
proposed according to which a first network is able to retrieve an
unanswered call before the call is forwarded to a messaging service
by a second network, where the call is originally intended for a
destination in the first network and has been transferred to a
destination in the second network.
[0006] According to the method, a first communications network
detects calls directed to a destination in the first network and
redirects at least some of the calls to a destination in a second
network (e.g. on no answer from a destination in the first
network). The first network operates in two phases. In a first
phase, for a group of calls redirected to the second network, the
time delay before the call is answered in the second network is
recorded. When a number of time delays have been recorded, a delay
period is set to a value less than the maximum value of the
recorded time delays. In a second phase, for a second group of
calls redirected to the second network subsequent to the calls of
the first group, when a call of the second group is not answered in
the second network within the delay period, the call is redirected
to a message service or other, alternative destination associated
with the first network.
[0007] The maximum time delay before calls are answered in the
second network will be equal to or less than the delay in the
second network before a call is transferred to a messaging service.
Setting the delay period at which a call is retrieved to the first
network to a value less than this maximum means that subsequent
calls will be retrieved by the first network before they are
transferred to a messaging service by the second network.
[0008] The first communications network comprises a network
controller for detecting calls directed to a destination in the
first network and for redirecting at least some of the calls to a
destination in a second network (e.g. on no answer in the first
network). The network controller comprises a first timer for
recording time delays before each call of a group of calls
redirected to the second network is answered in the second network
and a second timer which is set to a delay period value less than
the maximum value of the time delays recorded by the first timer.
The network controller also comprises a switch for redirecting an
unanswered call to a message service associated with the first
network, where a call from a second a group of calls (comprising
calls redirected to the second network subsequent to the calls of
the first group) is an unanswered call when it is not answered in
the second network within the delay period.
[0009] The switch is configured to retrieve to the first network a
call redirected to the second network when the call is not answered
within the delay period. The delay period is set to a value less
than the maximum recorded value of time delay before a call
redirected to the second network is answered in the second network
so that subsequent calls will be retrieved by the first network
before they are transferred to a messaging service by the second
network.
[0010] It is possible that the user or service provider removes or
disables the messaging service provided by the second network
(effectively equivalent to an infinite value of delay before
transfer-to-messaging-service) or, simply, increases the delay
before redirection to the messaging service. Advantageously,
according to one aspect of the invention, the call control system
is able to adapt to increases in the delay in the second network
before a call is forwarded to a messaging system in the second
network.
[0011] Similarly, it is possible that the user or service provider
decreases the delay before redirection to the messaging service.
Advantageously, according to one aspect of the invention, the call
control system is able to adapt to decreases in the delay in the
second network before a call is forwarded to a messaging system in
the second network.
[0012] Under certain circumstances a call, having been redirected
to the second network, may be immediately forwarded in the second
network to an alternative destination (e.g. voicemail). When a
subscriber does not want to be disturbed and has instructed their
network operator to divert all calls to their handset in the second
network to voicemail without first ringing the subscriber's
handset, a call, having been redirected to the second network, is
immediately forwarded to a messaging service in the second network.
Similarly, when the subscriber's handset in the second network is
switched off or is out of range of the wireless network, a call,
having been redirected to the second network, is immediately
forwarded to a messaging service in the second network. In such
cases the delay in the second network before a call is forwarded to
the messaging service will be much shorter. Advantageously,
according to a further aspect of the invention, when a call of the
second set redirected to the second network is answered in the
second network within a second delay period shorter than the delay
period, the call is redirected in the first network to an
alternative destination associated with the first network.
According to a further aspect, the timer controller is arranged in
use to set a third timer to a second delay period shorter than the
delay period and the switch is arranged in use to redirect a call
that is answered in the second network within the second delay
period to an alternative destination associated with the first
network.
[0013] For the avoidance of doubt, according to the present
invention, redirection of calls to the alternative destination
associated with the first network is controlled from the first
network.
[0014] To aid understanding of the invention, embodiments will now
be described by way of example only, with reference to the
accompanying drawings in which:
[0015] FIGS. 1a and 1b show schematics of communications systems to
which the invention may be applied;
[0016] FIG. 2 shows a schematic of a server for implementing the
invention.
[0017] FIG. 1a shows a schematic of communications system 10
comprising GSM mobile network 12, IMS mobile network 16 and
wire-line PSTN 18. Three handsets are shown, each for use with a
different communications network. Conventional, wired handset 20 is
attached to provide telephone service via PSTN 18. Handset 22
operates in GSM mode via GSM network 12 and handset 24 operates in
Wi-Fi mode via IMS network 16.
IP Multimedia Subsystem (IMS) Network
[0018] FIG. 1a shows IMS network 16 in detail (GSM network 12 is
shown in detail in FIG. 1b). As shown in FIG. 1a, Wi-Fi handset 24
exchanges radio signals with Wi-Fi access point 26 to IMS network
16. Wi-Fi handset 24 needs to register with the IMS network in
order to send and receive messages.
[0019] Proxy CSCF (P-CSCF) 160 in IMS network 16 forms the
interface between Wi-Fi handset 24 and the rest of the IMS network.
P-CSCF 160 authenticates the user and acts as a proxy, routing the
traffic from Wi-Fi handset 24 to Interrogating-CSCF (I-CSCF) 162.
I-CSCF 162 controls IMS connections destined to users subscribed to
the network operator of IMS network 16, or to roaming users
currently located within that network operator's service area.
I-CSCF 162 acts as the administrative boundary of the IMS network
(as P-CSCF 160 could be in a roaming partner's network--FIG. 1a
showing a simplified view). Wi-Fi handset 24 connects to P-CSCF 160
via Wi-Fi access point 26. P-CSCF 160 authenticates Wi-Fi handset
24 (via I-CSCF 162 using information from Home Subscriber Server
(HSS) 168).
[0020] HSS 168 comprises a database containing subscription-related
information to support call control in IMS network 16. HSS 168
provides support for authentication, authorisation,
naming/addressing resolution, etc. To achieve this, HSS 168 stores
the following user related information: user identification,
numbering and addressing information; user security information:
network access control information for authentication and
authorization; user location information at inter-system level. HSS
168 supports the user registration.
[0021] Thereafter P-CSCF 160 acts as a proxy forwarding SIP traffic
from handset 24 to I-CSCF 162. I-CSCF 162 locates HSS 168(via a
subscriber location function (SLF not shown)) and routes the SIP
traffic from Wi-Fi handset 24 to the appropriate instance of
Serving-CSCF (S-CSCF) 166.
[0022] S-CSCF 166 maintains the session state required by the
operator of IMS network 16 in support of session control services
for Wi-Fi handset 24. S-CSCF 166 is the main call control element
of IMS network 16. It downloads from HSS 168 the user profile which
contains a set of triggers that may cause SIP messages to be routed
to application servers. Call control functions are implemented by
the definition of these triggers and the functions provided by the
associated application servers. In the example of FIG. 1a, a
trigger might be to route the SIP "invite" message for voice calls
to voicemail server 172 if the call hasn't been answered after a
specified interval. It is more likely that this function would be
implemented by Voice Call application server 178, rather than in
S-CSCF 166 itself.
[0023] We now consider the placing of an outgoing call and the
receipt of an incoming call in IMS network 16.
Outgoing Call from Wi-Fi Handset via IMS Network.
[0024] Wi-Fi handset 24 sends a SIP "invite" message to P-CSCF 160.
The "invite" message is routed via P-CSCF 160 and I-CSCF 162 to
S-CSCF 166. S-CSCF 166 matches the "invite" message to a trigger
and, as a result, may forward the "invite" message to voice call
server 178. Connection between IMS network 16 and GSM network 12 is
effected via PSTN 18. If the called subscriber is located on GSM
network 12, the invite message is redirected to the Breakout
Gateway Control Function (BGCF) 176 that is connected to PSTN 18.
BGCF 176 selects the appropriate Media Gateway Control Function
(MGCF) 154 for the selected PSTN 18. MGCF 154 controls the parts of
the call state that pertain to connection control for media
channels in MGW 156. Media Gateway (MGW) 156 terminates bearer
channels from PSTN 18. MGW 156 may also support media conversion,
bearer control and payload processing. Signalling Gateway (SGW) 152
provides a signalling interface with PSTN 18. The call is thus
routed to the PSTN which then routes the call to the Gateway Mobile
Switching Centre (GMSC) of the relevant GSM network (as described
in more detail, below). It would also be possible for the IMS and
mobile networks to be connected directly to each other.
Incoming Call to Wi-Fi Handset via IMS Network
[0025] We describe next, an example of a call received at IMS
network 16 from PSTN 18.
[0026] An incoming call (from PSTN 18, for example) for handset 24
will result in a SIP "invite" message arriving at the instance of
S-CSCF (represented in the drawings by S-CSCF 166) allocated to the
handset. In the case of a call input from PSTN 18, the call is
input via the appropriate instances of BGCF 176 and MGCF 154.
S-CSCF 166 downloads a user profile for the intended recipient from
the appropriate instance of HSS (represented in the drawings by HSS
168). The user profile includes initial filter criteria including
trigger point data which specify how to handle SIP messages
matching specified criteria (e.g.: relating to inbound SIP "invite"
messages addressed to the user, as opposed to outgoing SIP "invite"
messages). As the incoming call is a voice call, S-CSCF 166 finds a
match in the filter criteria trigger points, which indicate that
the SIP "invite" message is to be forwarded to voice call server
178, incorporating Session Initiation Protocol Application Server
(SIP-AS) 164.
[0027] Voice call server 178 checks whether the IMS user is
currently registered, and, if so, forwards the SIP "invite" message
to the SIP .sup.-client(s) running on the registered user's Wi-Fi
handset 24. If the call request is answered by the client in
response to the SIP "invite" message, the call is set up
accordingly. However, if the user is not currently registered or
the user declines the call or fails to answer within a specified
period, voice call server 178 forwards the SIP "invite" message to
an alternative destination in (for example) GSM network 12 as
described above under "Outgoing Call from Wi-Fi handset". Voice
call server 178 knows where to re-direct the call based on
information contained in the user profile. Voice call server 178
then waits until it receives a SIP "ringing" message from GSM
network 12 at which point it starts a timer.
[0028] Operation of voice call server 178 from this point in the
call set-up process will depend on whether the voice call server is
operating in a first phase or a second phase according to the
invention.
PHASE 1
[0029] In the first phase, voice call server 178 monitors, through
notifications provided by GSM network 12, the behaviour of the GSM
network upon receiving a call redirected from IMS network 16. The
notifications take the form of SIP "ringing" and "answer" messages.
Receipt of the SIP "ringing" message has been described, above. The
SIP "answer" message (i.e.: "200 OK") may be triggered by the call
being answered in GSM network 12 either by a user (ideally the
intended subscriber) actually answering the ringing phone or by a
messaging service, such as voicemail function 140. According to a
preferred embodiment, voice call server 178 stops the timer on
receipt from GSM network 12 of the "answer" message and stores the
measured time-to-answer delay in a store dedicated to the user, for
example, in hard disk drive or volatile semiconductor memory device
(as illustrated in FIG. 2 by storage device 72 and RAM 75).
[0030] At the end of the first phase (for example, after a
specified number of time-to-answer delay values have been recorded
for the user) voice call server 178 determines the maximum value of
delay before answer for the user exhibited by GSM network 12. Given
the presence of messaging service 140 in GSM network 12, this
maximum value of delay before answer will normally correspond to
(and, in any case, not be greater than) the delay before the GSM
messaging service answers a call redirected from IMS network 16.
Voice call server 178 processes the recorded delay values and
defines a delay period equal to the maximum recorded value of delay
before answer less a specified margin (e.g. one second, or one
ring-period) and stores this value for future use. Suitable storage
may be found in the user profile in HSS 168, or alternatively, in a
separate database managed by voice call server 178.
PHASE 2
[0031] In the second phase, voice call server 178 continues to
monitor, through the SIP "ringing" and "answer" messages received
from GSM network 12, the behaviour of GSM network 12 upon receipt
of a call redirected from IMS network 16. In the second phase,
however, voice call server 178 runs a second timer set to the delay
period determined at the end of the first phase. The second timer
is started on receipt of an SIP "ringing" message and either
generates a signal or is checked to indicate when the delay period
elapses.
[0032] Successful Redirection Case (Call to Wi-Fi handset
redirected to GSM). For the successful redirection case, voice call
server 178 receives notification from GSM network 12 that the call
has been answered at the alternative destination in GSM network 12
before the timer has indicated that the delay period has elapsed.
In this case, no further action is taken for that call, which is
assumed to have been correctly terminated in GSM network 12.
[0033] Unsuccessful Redirection Case (Call to Wi-Fi handset
redirected to GSM). For the unsuccessful redirection case, however,
the timer indicates that the delay period for the call has elapsed
before any "answer" message for that call has been received from
GSM network 12. Voice call server 178 determines that the
unanswered call should be diverted back to a messaging service
(i.e.: voicemail function 170) in IMS network 16 that is associated
with the Wi-Fi handset that was the original destination for the
call. This is done to prevent the call being answered by a
messaging service (i.e.: voicemail function 140) in the "wrong"
network, i.e.: in this case, GSM network 12. Voice call server 178
cancels the forwarded call to the GSM network (sends a SIP "bye"
message), dials the number for IMS messaging service 170 and
diverts the call to the messaging service. The IMS messaging
service accepts the diverted call request and the caller is
connected to voicemail server 172.
Minimum Delay Timer (Incoming Call to Wi-Fi Handset)
[0034] A further embodiment addresses the case where the mobile
terminal in GSM network 12, to which the call is redirected, is
unreachable. When a terminal is marked as unreachable, GSM network
12 does not even attempt to put the call through to the terminal
but immediately forwards it to the messaging service. (e.g.
voicemail). An additional, minimum-delay timer (not shown) is
provided according to this embodiment to detect calls which are
answered in GSM network 12 within a very short time (the
minimum-delay period) of the call being redirected to GSM network
12. The minimum-delay timer is additional to the maximum-delay
timer, described above. The minimum-delay period is selected to be
longer than the delay required to forward a call to the messaging
service of GSM network 12 when the mobile terminal in GSM network
12, to which the call is redirected, is marked as unreachable.
[0035] Successful Redirection Case (Minimum Delay Timer). For the
successful redirection case, voice call server 178 receives
notification from GSM network 12 that the call has been answered at
the alternative destination in GSM network 12 after the
minimum-delay timer has indicated that a pre-specified minimum
delay period has elapsed and before the maximum-delay timer has
indicated that the delay period has elapsed. In this case, no
further action is taken for that call, which is assumed to have
been correctly terminated in GSM network 12.
[0036] Unsuccessful Redirection Case (Minimum Delay Timer). For the
unsuccessful redirection case, however, voice call server 178
receives notification from GSM network 12 that the call has been
answered at the alternative destination before the specified
minimum delay period for the call has elapsed. Voice call server
178 cancels the forwarded call to the. GSM network (sends a SIP
"bye" message), dials the number for IMS messaging service 170 and
diverts the call to the messaging service. The IMS messaging
service accepts the diverted call request and the caller is
connected to voicemail server 172. This is done to prevent the
call, originally directed to a destination in IMS network 16 being
answered by a messaging service (i.e.: voicemail function 140) in
GSM network 12.
GSM Network
[0037] FIG. 1b shows a schematic of communications system 10, as in
FIG. 1a but now with details of GSM network 12 shown.
[0038] GSM handset 22 exchanges radio signals with base transceiver
station (BTS) 120, operating under control of base station
controller (BSC) 122 of GSM network 12. GSM network 12 also
comprises home location register (HLR) 124 which includes a
database (not shown) of information on users of the mobile network.
HLR 124 stores user information, including location, account status
and preferences and is maintained by the network operator
subscribed to by the user. Both BSC 122 and HLR 124 interact with
mobile switching centre (MSC) 126, which is a switch used for call
control and processing. MSC 126 also serves as a point-of-access to
PSTN 18 via gateway mobile switching centre (GMSC) 130. MSC 126 is
associated with visitor location register (VLR) 125 which stores
information about all the mobiles that are currently under the
control of MSC 126.
[0039] GSM network 12 uses HLR 124 to obtain up-to-date location
information about a user so that a call can be delivered to the
user regardless of their location in the telephone network at the
time. GMSC 130 provides an interface with PSTN 18 and determines
the appropriate MSC 126 to which an incoming call to a mobile user
should be directed (i.e. the MSC 126 at which the called user is
currently recorded as being located). GSM network 12 queries HLR
124 to determine which MSC (out of a plurality represented in FIG.
1 by MSC 126) is currently providing service to the user.
Successful Call to GSM.
[0040] A subscriber initiates a call in an originating network
(e.g. IMS 16, PSTN 18 or another mobile network--not shown) to a
subscriber in GSM network 12 by dialling the GSM phone number
allocated to the called subscriber. The originating network uses
the GSM phone number to locate the GMSC for the service provider
serving the called subscriber. Once the appropriate GMSC
(represented in the drawings by GMSC 130) has been identified, the
originating network sends to it an ISUP "initial address
message".
[0041] GMSC 130 requests routing information for the called GSM
subscriber from the Home Location Register (represented in the
drawings by HLR 124) allocated to the called subscriber. HLR 124
uses the dialled number carried in the "initial address" message to
locate a record for the subscriber. The SS7 address for the MSC and
VLR serving the subscriber (represented in the drawings by MSC 126
and VLR 120 is obtained from this record.
[0042] HLR 124 then contacts MSC/VLR 126,125 serving the subscriber
and requests the assignment of a temporary roaming phone number to
the called subscriber. In response to the request from HLR 124,
MSC/VLR 126,125 allocates a temporary roaming phone number
(MSR--Mobile Station Roaming Number) to the called subscriber and
passes it to HLR 124, which passes it in turn to GMSC 130. GMSC 130
uses the temporary roaming phone number to route the call to
MSC/VLR 126,125.
[0043] The destination phone is paged, via all base station
controllers (BSC) connected to MSC 126. Each BSC (represented in
the drawings by BSC 122) connected to MSC 126 sends a "page"
message to all cells that serve the subscriber's current location
area. The base transceiver stations (represented in the drawings by
BTS 120) for each of these cells broadcast the "page" message
received from their BSC on a dedicated paging channel which all
mobile phones listen to every few seconds.
[0044] The destination phone, on finding that an identifier
specified in a "page" message matches its own identifier,
acknowledges the receipt of the call setup request. MSC 126
receives the acknowledgement and sends an ISUP "address complete"
message to GMSC 130, which forwards it to the originating network.
When the called subscriber answers the call, an ISUP "answer"
message is sent by MSC 126 to GMSC 130. The call is now set up.
[0045] The above description relates to a call successfully
connected through to a destination in GSM network 12 from a source
located in an originating network outside of GSM network 12, for
example the originating network being PSTN 18.
Unsuccessful Call to GSM.
[0046] We shall now describe how the present invention, for example
operating on GMSC 130, enables a call, initially directed (as
described, above) to an original destination in mobile GSM network
12 and then redirected to an alternative destination in a second
network (e.g.: PSTN 18) and subsequently, upon failure to answer
the call in the second network, to be retrieved to GSM network 12
and redirected to a messaging service associated with the original
destination in GSM network 12. Rather than being forwarded to a
messaging service associated with the second network, which might
cause inconvenience to the called subscriber, the call is
terminated at a messaging service associated with the called
subscriber's handset that was the original destination of the
call.
[0047] The call may be redirected away from the original
destination in GSM network 12 for a number of reasons. The user may
not be available to respond to the call. The mobile terminal
associated with the original destination may be busy or not on-line
so that no valid response is received at MSC 126 to the "page"
messages issued by the BSCs. In such a case, i.e.: where no
response is received to the "page" messages, GSM network 12 may be
provided with an alternative destination, e.g. a "call forward
unavailable" number. For the purposes of the present embodiment, we
shall describe the case where the "call forward unavailable" number
is set to a number registered in PSTN 18.
[0048] According to this embodiment, MSC 126 routes the
unsuccessful call via GMSC 130 to PSTN 18, where the call setup
request is put through to the alternative destination according to
the "call forward unavailable" number. MSC 126 receives
notification from PSTN 18 that the call setup request has been put
through to the alternative destination (e.g.: that ringing signal
has been applied to the selected phone in PSTN 18). The
notification takes the form of an ISUP "address complete" message.
MSC 126 initiates a timer (not shown) on receipt from PSTN 18 of
this message.
[0049] Operation of GMSC 130 from this point in the call set-up
process will depend on whether the GSMC is operating in a first
phase or a second phase according to the invention.
PHASE 1
[0050] In the first phase, MSC 126 monitors, through notifications
provided by PSTN 18, the behaviour of PSTN 18 upon receiving a call
redirected from GSM network 12. The notifications take the form of
ISUP "address complete" and "answer" messages. Receipt of the ISUP
"address complete" message has been described, above. The ISUP
"answer" message may be triggered by the call being answered in
PSTN 18 either by a user (ideally the intended subscriber) actually
answering the ringing phone or by a messaging service, such as an
answer-phone. According to a preferred embodiment, MSC 126 stops
the timer on receipt from PSTN 18 of the "answer" message.
[0051] Still in the first phase, MSC 126 informs GMSC 130 of the
time intervals recorded between the receipt of the ISUP "address
complete" and "answer" messages pertaining to each redirected call.
GMSC 130 creates a record of the delays before each redirected call
is answered in PSTN 18 and determines the maximum value of delay
before answer. GMSC 130 records the delay values either in hard
disk drive or volatile semiconductor memory device (as illustrated
in FIG. 2 by storage device 72 and RAM 75). Given the presence of a
messaging service in PSTN 18, this maximum value of delay before
answer will normally correspond to (and, in any case, not be
greater than) the delay before the PSTN messaging service (not
shown) answers a call. After having received a quantity of delay
times, GMSC 130 provides MSC 126 with a delay period calculated to
be less than the maximum recorded value of delay before answer. MSC
126 stores the delay period provided by GMSC 130 either in hard
disk drive or volatile semiconductor memory device (as illustrated
in FIG. 2 by storage device 72 and RAM 75).
PHASE 2
[0052] In the second phase, GMSC 130 continues to monitor, through
the ISUP "address complete" and "answer" messages received from
PSTN 18, the behaviour of PSTN 18 upon receipt of a call redirected
from GSM network 12. In the second phase, however, MSC 126 runs a
second timer set to the delay period determined by GMSC 130. The
second timer is started on receipt of an "address complete" message
and either generates a signal or is checked to indicate when the
delay period elapses.
Successful Redirection Case (Incoming Call to GSM Handset).
[0053] For the successful redirection case, MSC 126 receives
notification from PSTN 18 that the call has been answered at the
alternative destination in PSTN 18 before the timer has indicated
that the delay period has elapsed. In this case, no further action
is taken for that call, which is assumed to have been correctly
terminated in PSTN 18.
Unsuccessful Redirection Case (Incoming Call to GSM Handset).
[0054] For the unsuccessful redirection case, however, the timer
indicates that the delay period for the call has elapsed before any
"answer" message for that call has been received from PSTN 18. In
this case, MSC 126 determines that the call should now be diverted
back to messaging service 140 in GSM network 12 associated with the
mobile phone that was the original destination of the call. This is
done to prevent the call being answered by a messaging service in
PSTN 18. MSC 126 dials the number for GSM messaging service 140--in
a similar way to the traditional mobile network diverting a call to
a call forward number--and diverts the call to the messaging
service.
[0055] According to a preferred embodiment, the delay period
determined by GMSC 130 is stored in HLR 124 allocated to the called
subscriber (alongside other "call forward" timeouts for that
subscriber, i.e. timeouts for call forward busy, call forward
unreachable etc.).
Minimum Delay Timer (Incoming Call to GSM Handset).
[0056] A further embodiment addresses the case where the call,
having been redirected to PSTN 18, is immediately forwarded in PSTN
18 to a messaging service (e.g. voicemail). This could occur when
the subscriber does not want to be disturbed and has instructed
PSTN 18 to divert all calls to the destination to voicemail without
first ringing the subscriber's handset. An additional,
minimum-delay timer (not shown) is provided according to this
embodiment to detect calls which are answered in PSTN 18 within a
very short time (the minimum-delay period) of the call being
redirected from GSM network 12. The minimum-delay timer is
additional to the maximum-delay timer, described above. The
minimum-delay period is selected to be longer than the delay
required to forward a call to the messaging service of PSTN 18 when
this is done immediately on the call arriving in PSTN 18.
[0057] As will be understood by those skilled in the art, GMSC 130,
MSC 126 and voice call server 178, described above may be
implemented as one or more commercially available server or similar
general-purpose processing means, as illustrated in FIG. 2. FIG. 2
shows a typical architecture for a server suitable for implementing
the network controller of the invention according to a further
embodiment of the invention. In practice, a number of such servers
will typically be required. The server comprises a central
processing unit (CPU) 70 for executing software programs and
managing and controlling the operation of the processing means. The
CPU 70 is connected to a number of devices via a bus 71, the
devices including one or more storage devices 72, for example: a
hard disk drive, floppy disk drive, optical disk drive and/or
magnetic tape drive and memory devices including ROM 74 and RAM 75
for storing system and application software and values for delay
time and delay period. The server further includes communications
interfaces 77 for interfacing to external network components (for
example other components within IMS network 16 or GSM network 12).
The server can also include user input/output devices such as a
mouse and keyboard (not shown) connected to the bus 71 via an
input/output port 76, as well as a display 78. It will be
understood by the skilled person that the above described
architecture is not limiting, but is merely an example of typical
server architecture. It will be further understood that the
described server has all the necessary operating and application
software to enable it to fulfil its purpose.
[0058] As will be understood by those skilled in the art, the
invention may be implemented in software loaded onto one or more
general purpose computers, as illustrated by way of example in FIG.
2. Any or all of the software may be contained on a computer
program product, including optically readable or magnetic media,
such as a floppy disc, CD-ROM, or magnetic tape so that the program
can be loaded onto one or more general purpose computers.
[0059] The above embodiments are to be understood as illustrative
examples of the invention. Further embodiments of the invention are
envisaged and will be evident to the skilled reader. It is to be
understood that any feature described in relation to any one
embodiment may be used alone, or in combination with other features
described, and may also be used in combination with one or more
features of another of the embodiments, or any combination of the
embodiments. Furthermore, equivalents and modifications not
described above may also be employed without departing from the
scope of the invention, which is defined in the accompanying
claims.
[0060] Although described above with reference to GSM and Wi-Fi,
the skilled reader would understand that the call control
arrangements, described above, may equally be applied to a code
division multiple access (CDMA), time division multiple access
(TDMA), or other types of mobile communications network or, indeed,
to various forms of fixed network. Although described above with
reference to calls being redirected--on no answer in the second
network--to a message service, the invention is equally applicable
where the destination for calls redirected on no answer in the
second network is another form of telephony device such as a
telephone terminal or pre-recorded announcement. Similarly, the
destination of calls retrieved from the second network is not
limited to a message service and may, alternatively, comprise
another form of telephony device such as a telephone terminal
(e.g.: a "parental hotline" to a parent of the owner of the called
terminal) or pre-recorded announcement. The two timers, described
above, could be located elsewhere than the MSC or voice call server
(depending on the network). The skilled reader would appreciate
that different means to allow a first network to monitor processing
activity in a second network relating to a call redirected from the
first network, may be appropriate, depending on the different types
of network and their interaction. The measurement of
delays-to-answer in the second network may be started from a number
of reference points or from a range of events, including the
transfer by the first network of the call to the second network.
Reference in the above to a handset will be understood to include
any suitable form of communications terminal, including
conventional telephones and telephone-enabled devices such as
portable computers. Determination of a value for the delay period
to be used in the second phase could involve a variety of
statistical treatments of measured values of delay time, e.g.
taking the average of the highest n values or smoothing to reduce
the influence of spurious values.
Abbreviations
[0061] BGCF Breakout Gateway Control Function
[0062] BSC Base Station Controller
[0063] BTS Base Transceiver Station
[0064] CSCF Call Session Control Function
[0065] GMSC Gateway Mobile Switching Centre
[0066] HLR Home Location Register
[0067] HSS Home Subscriber Server
[0068] I-CSCF Interrogating-CSCF
[0069] MGCF Media Gateway Control Function
[0070] MGW Media Gateway
[0071] MSC Mobile Switching Centre
[0072] P-CSCF Proxy CSCF
[0073] PSTN Public Switched Telephone Network
[0074] S-CSCF Serving-CSCF
[0075] SGW Signalling Gateway
[0076] SIP Session Initiation Protocol
[0077] SIP-AS SIP Application Server
* * * * *